selftests: ktap_helpers: Add a helper to finish the test

Similar to the C counterpart, keep track of the number of test cases in
the test plan and add a helper function to be called at the end of the
test to print the results and exit with the corresponding exit code.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

selftests: ktap_helpers: Add a helper to abort the test

Similar to the C counterpart, add a helper function to abort the
remainder of the test.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

selftests: ktap_helpers: Add helper to pass/fail test based on exit code

Similar to the C counterpart, add a helper function that runs a command
and passes or fails the test based on the result.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

selftests: ktap_helpers: Add helper to print diagnostic messages

Similar to the C counterpart, add a helper to print a diagnostic
message.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

selftests: Move KTAP bash helpers to selftests common folder

Move bash helpers for outputting in KTAP format to the common selftests
folder. This allows kselftests other than the dt one to source the file
and make use of the helper functions.
Define pass, fail and skip codes in the same file too.

Signed-off-by: Laura Nao <laura.nao@collabora.com>
Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>