Adaptions for Ubuntu Backend compatibility

There were a couple of minor adjustments needed in order to run a proper cvmfs backend on Ubuntu:
* Disable hardlink creation restrictions of yama LSM (kernel.yama.protected_nonaccess_hardlinks)
* apache switch on/off through `service` instead of `httpd` (should be portable)
* pushd/popd are bashisms; replaced them by pushdir/popdir wrapper functions (Note: they do not implement an actual stack since I don't need that behavior)

Additionally I needed to install the following packages and run the following commands before installation to make it work:

For installation:
- git
- cmake
- g++
- libfuse-dev
- libssl-dev

For Deployment:
- autofs
- attr

- Run `sudo cvmfs_config setup`
- Run `sudo cp -arp /etc/apache2/mods-available/headers.load  /etc/apache2/mods-enabled/headers.load`
- Run `sudo cp -arp /etc/apache2/mods-available/expires.load  /etc/apache2/mods-enabled/expires.load`

For Test system:
- cpanminus
- libzmq-dev
- uuid-dev
- liburi-perl
- Run `sudo cpanm ZeroMQ`
- Run `sudo mkdir /var/log/cvmfs-test`