Follow symlinks when searching for binaries with allowed setuid in test

Ubuntu 14.04 sudoedit is a symbolic link

Signed-off-by: Maria Shaldibina <mariash@pivotallabs.com>
Configure /etc/dhcp/dhclient.conf by default

Ubuntu 14.04 uses dhcp config located at /etc/dhcp/dhclient.conf.
Ubuntu 10.04 is using /etc/dhcp3/dhclient.conf. Check if dhcp3 config is
present and configure it instead. When restarting dhclient kill process
dhclient which is the same for Ubuntu 14.04 and Ubuntu 10.04.

Signed-off-by: Maria Shaldibina <mariash@pivotallabs.com>
Use operating system version in stemcell building vm Vagrantfile

Signed-off-by: Maria Shaldibina <mariash@pivotallabs.com>