sysutils/zap: Update to version 0.5.0

Changelog:

• Use getops for option handling.
• Create snapshots again when a scrub is in progress.
• Let the -r flag be specified for individual datasets.
  • To handle parsing the '-r' flags, the create function was broken off into two functions: create_parse() and create(). create() creates one snapshot per call.
• Created helper functions pool_ok and pool_scrub.
• Minor changes to warning messages.
• POSIX sh does not support local, so initialize variables intended to be local to a function.

Approved by: swills (mentor)
Differential Revision: https://reviews.freebsd.org/D8511