conditionally install wget if not present

so that we are not wastefully calling yum every time

Reference issue: http://tracker.ceph.com/issues/9265

    # new behavior does not install wget if present:
    
    (ceph-deploy)papaya ~/tmp/foo ᓆ ssh node2 which wget
    /usr/bin/wget
    (ceph-deploy)papaya ~/tmp/foo ᓆ ceph-deploy install node2
    [ceph_deploy.conf][DEBUG ] found configuration file at: /Users/alfredo/.cephdeploy.conf
    [ceph_deploy.cli][INFO  ] Invoked (1.5.14): /Users/alfredo/.virtualenvs/ceph-deploy/bin/ceph-deploy install node2
    [ceph_deploy.install][DEBUG ] Installing stable version firefly on cluster ceph hosts node2
    [ceph_deploy.install][DEBUG ] Detecting platform for host node2 ...
    [node2][DEBUG ] connected to host: node2
    [node2][DEBUG ] detect platform information from remote host
    [node2][DEBUG ] detect machine type
    [ceph_deploy.install][INFO  ] Distro info: CentOS 6.4 Final
    [node2][INFO  ] installing ceph on node2
    [node2][INFO  ] Running command: sudo yum clean all
    [node2][DEBUG ] Loaded plugins: fastestmirror, priorities
    [node2][DEBUG ] Cleaning repos: Ceph Ceph-noarch base calamari ceph-source ceph_deploy epel
    [node2][DEBUG ]               : extras foo updates
    [node2][DEBUG ] Cleaning up Everything
    [node2][DEBUG ] Cleaning up list of fastest mirrors
    [node2][DEBUG ] find the location of an executable
    [node2][INFO  ] adding EPEL repository
    [node2][INFO  ] Running command: sudo wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
    [node2][WARNIN] --2014-09-12 17:39:19--  http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
    [node2][WARNIN] Resolving dl.fedoraproject.org... 209.132.181.25, 209.132.181.26, 209.132.181.27, ...
    [node2][WARNIN] Connecting to dl.fedoraproject.org|209.132.181.25|:80... connected.
    [node2][WARNIN] HTTP request sent, awaiting response... 200 OK
    [node2][WARNIN] Length: 14540 (14K) [application/x-rpm]
    ...

    # we now remove wget to see if that changes anything:
    (ceph-deploy)papaya ~/tmp/foo ᓆ ceph-deploy pkg --remove wget node2
    [ceph_deploy.conf][DEBUG ] found configuration file at: /Users/alfredo/.cephdeploy.conf
    [ceph_deploy.cli][INFO  ] Invoked (1.5.14): /Users/alfredo/.virtualenvs/ceph-deploy/bin/ceph-deploy pkg --remove wget node2
    [node2][DEBUG ] connected to host: node2
    [node2][DEBUG ] detect platform information from remote host
    [node2][DEBUG ] detect machine type
    [ceph_deploy.pkg][INFO  ] Distro info: CentOS 6.4 Final
    [node2][INFO  ] removing packages from node2
    [node2][INFO  ] Running command: sudo yum -y -q remove wget

    # and ensure it is really not there
    (ceph-deploy)papaya ~/tmp/foo ᓆ ssh node2 which wget
    which: no wget in (/usr/local/bin:/bin:/usr/bin)

    # try installing ceph again and see if it installs wget (it doesn't)
    (ceph-deploy)papaya ~/tmp/foo ᓆ ceph-deploy install node2
    [ceph_deploy.conf][DEBUG ] found configuration file at: /Users/alfredo/.cephdeploy.conf
    [ceph_deploy.cli][INFO  ] Invoked (1.5.14): /Users/alfredo/.virtualenvs/ceph-deploy/bin/ceph-deploy install node2
    [ceph_deploy.install][DEBUG ] Installing stable version firefly on cluster ceph hosts node2
    [ceph_deploy.install][DEBUG ] Detecting platform for host node2 ...
    [node2][DEBUG ] connected to host: node2
    [node2][DEBUG ] detect platform information from remote host
    [node2][DEBUG ] detect machine type
    [ceph_deploy.install][INFO  ] Distro info: CentOS 6.4 Final
    [node2][INFO  ] installing ceph on node2
    [node2][INFO  ] Running command: sudo yum clean all
    [node2][DEBUG ] Loaded plugins: fastestmirror, priorities
    [node2][DEBUG ] Cleaning repos: Ceph Ceph-noarch base calamari ceph-source ceph_deploy epel
    [node2][DEBUG ]               : extras foo updates
    [node2][DEBUG ] Cleaning up Everything
    [node2][DEBUG ] Cleaning up list of fastest mirrors
    [node2][DEBUG ] find the location of an executable
    [node2][INFO  ] Running command: sudo yum -y install wget
    [node2][DEBUG ] Loaded plugins: fastestmirror, priorities
    [node2][DEBUG ] Determining fastest mirrors
    [node2][DEBUG ]  * base: reflector.westga.edu
    [node2][DEBUG ]  * epel: mirror.steadfast.net
    [node2][DEBUG ]  * extras: mirror.cogentco.com
    [node2][DEBUG ]  * updates: yum.tamu.edu
    ...