[3782] Test isolation problem in test/ral/providers/cron/crontab.rb

The test in question (test_parse_line) was nondeterministic because it
was relying on the sort order of a Hash whose keys were symbols. When
the sort order caused a blank line to appear at the end of the file
under test, the blank line was elided by the crontab parser, causing a
failure.

Modified the test to execute in a deterministic order that doesn't
place the blank line at the end.