Tools: hv: vssdaemon: report freeze errors

When ioctl(fd, FIFREEZE, 0) results in an error we cannot report it
to syslog instantly since that can cause write to a frozen disk.
However, the name of the filesystem which caused the error and errno
are valuable and we would like to get a nice human-readable message
in the log. Save errno before calling vss_operate(VSS_OP_THAW) and
report the error right after.

Unfortunately, FITHAW errors cannot be reported the same way as we
need to finish thawing all filesystems before calling syslog().

We should also avoid calling endmntent() for the second time in
case we encountered an error during freezing of '/' as it usually
results in SEGSEGV.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Acked-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>