findmnt: add option to list all fs-independent flags

findmnt: add option to list all fs-independent flags

It might be useful for security auditing purposes list all possible
mount flags/options including default set which are normally not listed.

This patch adds "--vfs-all" option to list all fs-independent flags
on VFS-OPTIONS column, as well as libmount funcionality to accomplish
it.

i.e.:

$ findmnt -o VFS-OPTIONS
VFS-OPTIONS
rw,relatime
rw,nosuid,nodev,noexec,relatime
rw,nosuid,nodev,noexec,relatime
ro,nosuid,nodev,noexec
...

$ findmnt --vfs-all -o VFS-OPTIONS
VFS-OPTIONS
rw,exec,suid,dev,async,loud,nomand,atime,noiversion,diratime,relatime,nostrictatime,nolazytime,symfollow
rw,noexec,nosuid,nodev,async,loud,nomand,atime,noiversion,diratime,relatime,nostrictatime,nolazytime,symfollow
rw,noexec,nosuid,nodev,async,loud,nomand,atime,noiversion,diratime,relatime,nostrictatime,nolazytime,symfollow
ro,noexec,nosuid,nodev,async,loud,nomand,atime,noiversion,diratime,norelatime,nostrictatime,nolazytime,symfollow
...

[kzak@redhat.com: - cleanup coding style and comments]

Signed-off-by: Roberto Bergantinos Corpas <rbergant@redhat.com>
Signed-off-by: Karel Zak <kzak@redhat.com>