virstoragefile: Have virStorageFileResize use safezero

virstoragefile: Have virStorageFileResize use safezero

Currently virStorageFileResize() function uses build conditionals to
choose either the posix_fallocate() or syscall(SYS_fallocate) with no
fallback in order to preallocate the space in the newly resized file.

Since the safezero code has a similar set of conditionals modify the
resize and safezero code in order to allow the resize logic to make use
of safezero to unify the look/feel of the code paths.

Add a new boolean (resize) to safezero() to make the optional decision
whether to try syscall(SYS_fallocate) if the posix_fallocate fails because
HAVE_POSIX_FALLOCATE is not defined (eg, return -1 and errno == 0).

Create a local safezero_sys_fallocate in order to handle the resize
code paths that support that.  If not present, the set errno = ENOSYS
in order to allow the caller to handle the failure scenarios.

Signed-off-by: John Ferlan <jferlan@redhat.com>