test: Fixed running all tests together.

rake test:unit (which runs make check) runs the tests in isolation. That
takes long.

This enables running them all together which "rspec" alone does by
default.

The speedup is
  23s -> 9s  on a fast machine
  93s -> 24s on a slow machine

Also made tests independent of order they are run in (--order random).

Avoid redefining constants:
- move a constant outside a .each loop
- rename a constant
test helper: respect existing Y2DIR

to enable manual testing, specifying yast2.rpm paths with
`Y2DIR=... rspec ...`
test: RSpec 3 compatibility: avoid be_true, be_false.
test: pass a hash as intended, not a block

Ruby is readable, except when it is not.

This fixes
     Failure/Error: expect(Yast::SCR).
     ArgumentError:
       wrong number of arguments (0 for 1+)
which is quite cryptic. Running rspec -b/--backtrace reveals the problem
is in and_return.

This probably broke only with RSpec3.
test: Stubed out sleep(5).

Now they can all run in 4s total.
Merge branch 'master' into rspec
version + changelog
Merge pull request #243 from mvidner/rspec

Rspec speed up, enable library lookup in working copies.