Use alien_cache option for cvmfs in parrot
Change malloc to string_format for cvmfs options
Honor $TMPDIR for default value of pfs_temp_dir
Add --cvmfs-alien-cache command line option.
Cleanup cvmfs locks dir.

Now that the cvmfs locks dir pathname is not the same for every parrot
run, we need to remove it at the end of execution.
Merge branch 'parrot_alien_cache'

Fixes #298. Adds alien_cache option to cvmfs so that multiple instances of
parrot can access a cvmfs repository simultaneously, from the same machine.