Fix an out-of-order execution issue regarding pkg(8):

Fix an out-of-order execution issue regarding pkg(8):
- pkg(8) cannot be removed before subsequent reinvocations
- The PKG_CACHEDIR cannot be cleaned after the repo*.sqlite
  has been removed
- pkg(8) cannot be removed as a precursor to any of the other
  steps involved here

MFC after:	3 days
X-MFC-With:	r285722
X-MFC-Before:	10.2-{BETA3,RC1} (whichever happens next)
Sponsored by:	The FreeBSD Foundation