Add prompt if using --metadataignore argument with vgmetadatacopies.

Add prompt if using --metadataignore argument with vgmetadatacopies.

When using vgmetadatacopies value other than "umanaged" (0), prompt
the user if the usage of --metadataignore would change the value of
vgmetadatacopies.  The main 2 cases are:
1) pvchange --metadataignore
2) vgextend --metadataignore

We leave the prompt check in the tools, and do not change anything
if the user says 'n'.

Examples:
vgextend --metadataignore y vgtest /dev/loop0
Setting metadataignore will override preferred number of copies of VG vgtest metadata.
Are you sure? [y/n]: y
  No physical volume label read from /dev/loop0
  Physical volume "/dev/loop0" successfully created
  Volume group "vgtest" successfully extended

pvchange --metadataignore y /dev/loop3
Setting metadataignore on /dev/loop3 will override preferred number of copies of VG vgtest metadata.
Are you sure? [y/n]: y
  WARNING: Changing preferred number of copies of VG vgtest metadata from 3 to 2
  Physical volume "/dev/loop3" changed
  1 physical volume changed / 0 physical volumes not changed

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>