[lldb] Make TestDeletedExecutable more reliable
It seems that calling Popen can return to the caller before the started process has read all the needed information
from its executable. This means that in case we delete the executable while the process is still starting up,
this test will create a zombie process which in turn leads to a failing test. On my macOS system this happens quite frequently.
This patch fixes this by letting the test synchronize with the inferior after it has started up.
Reviewed By: davide
Subscribers: labath, friss, lldb-commits
Differential Revision: https://reviews.llvm.org/D64546