[lldb-mi] Fix bugs in target-select-so-path.test
- This patch fixes hanging of the test in case of using python3, changes callback function that will be called if the timer ends, changes python interpreter to %python that is set up by llvm-lit.
- Also, the test didn't work properly since it didn't contain a call of filecheck_proc.communicate(), that means that filecheck didn't run and its return code was equal to 0 in all cases.
Reviewers: teemperor, labath, tatyana-krasnukha, aprantl
Reviewed By: teemperor, labath
Subscribers: ki.stfu, lldb-commits
Differential Revision: https://reviews.llvm.org/D52498