Linux launch adjust

On Linux distros such as Arch .etc. Python 3 is installed as /usr/bin/python and Python 2 is installed as /usr/bin/python2.

Running pip2, or python2 on setup.py works perfectly, however the installed gmvault script detects GMVAULT_HOME as /usr/ and attempts to run /usr/bin/python which fails, leaving an error about the gmv module not being found.

This changes gmvault to prioritize the $GMVAULT_HOME/bin/python2 and falls back on $GMVAULT_HOME/bin/python.