Always use blocking lock for VGs and orphan locks.

Always use blocking lock for VGs and orphan locks.

Because we have now strong rule for lock ordering:
 - VG locks must be taken in alphabetical order
 - ORPHAN locks must be the last
vgs_locked() is now not needed.

This fixes problem with orphan locking, e.g.
vgremove VG1    |    vgremove VG2
lock(VG1)       |    lock(VG2)
lock(ORPHAN)    |    lock(ORPHAN) -> fail, non-blocking

https://bugzilla.redhat.com/show_bug.cgi?id=578413

(More similar places in code.)