Skip messages are not printed anymore with the new asynchronous execution policy

[vkarak]

Test:

@simple_test
class my_test(RunOnlyRegressionTest):
    x = variable(int, value=10)
    executable = 'echo'
    sanity_patterns = sn.assert_true(1)

    @run_after('init')
    def check_x(self):
        '''Test will not be listed or run if filtered here'''
        self.skip_if(self.x < 3, 'x is lower than 3')

    @run_before('run')
    def check_x2(self):
        '''Test will be skipped during runtime'''
        self.skip_if(self.x < 5, 'x is lower than 5')

Run:

reframe -c test.py -S valid_systems='*' -S valid_prog_environs='*' -n my_test -S x=4 -r

Output:

[----------] start processing checks
[ RUN      ] my_test @generic:default+builtin
[----------] all spawned checks have finished

[  PASSED  ] Ran 0/1 test case(s) from 1 check(s) (0 failure(s), 1 skipped)

The test is reported as skipped, but we should print a SKIP message as well.

[teojgo]

Fixed with #2400