disk/vfs: ensure guestfs capabilities

Ensures that guestfs is available and well configured. Also
when checking for capabilities this commit introduces an in-memory
flag to avoid repeating the process if succeeded.
If we are able to load guestfs but something wrong happens a fatal
error is raised.

DocImpact: We should add a not for ubuntu like systems that use
libguestfs to execute the command 'update-guestfs-appliance' for
configuring it.

Closes-Bug: #1275267
Closes-Bug: #1157922
Change-Id: I97b3a23829ea1f3aadfe08ca6448b35010d2f312
Merge "disk/vfs: ensure guestfs capabilities"