oeqa/runtime/stap: improve systemtap test

oeqa/runtime/stap: improve systemtap test

Split the test up into compile and execute phases, as the stap binary
is known to be quite memory-hungry and this can result in the probe
being unable to allocate enough memory for the buffers it needs.

If the test fails, dump the dmesg as any useful messages will be there.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>