test: test cherry-pick functionality and output separately

test: test cherry-pick functionality and output separately

Since v1.7.3-rc0~26^2~9 (revert: report success when using option
--strategy, 2010-07-14), the cherry-pick-many-commits test checks the
format of output written to the terminal during a cherry-pick sequence
in addition to the functionality.  There is no reason those have to
be checked in the same test, though, and it has some downsides:

 - when progress output is broken, the test result does not convey
   whether the functionality was also broken or not

 - it is not immediately obvious when reading that these checks are
   meant to prevent regressions in details of the output format and
   are not just a roundabout way to check functional details like the
   number of commits produced

 - there is a temptation to include the same kind of output checking
   for every new cherry-pick test, which would make future changes
   to the output unnecessarily difficult

Put the tests from v1.7.3-rc0~26^2~9 in separate assertions, following
the principle "test one feature at a time".

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>