* test: Add findmnt package
When testing mounts we can use findmnt --json output to parse the output
cleanly. The package provides only ParseOutput() now, but it can be
extended later to run the findmnt command.
* test: Support virtiofs mounts
Use findmnt command to get the mounted filesystem details cleanly.
We use the actual mount fstype instead of driver name check so we can
switch drivers to virtiofs without changing the test.
For virtiofs mount we skip options validation since we don't support
setting virtiofs options yet, and the options are not the same as 9p
options.
For 9p mounts the uid= and gid= flags were fixed to match the real flags
(dfltuid=,dfltgid=). The issue was hidden by imprecise string matching.
Nir Soffer