Bug 1596967 - In Android xpcshell tests, do not push tests to existing directory; r=bc

Currently the xpcshell harness ensures the remote scripts directory, /sdcard/tests/xpc, is
deleted, then re-creates it, then pushes to it. In this bug, confusion arises when a pre-push
check for directory existence intermittently fails (reports the directory does not exist
when in fact it does). Let's simplify this sequence by simply ensuring that the directory
has been deleted, then push to it.

Differential Revision: https://phabricator.services.mozilla.com/D53684

--HG--
extra : moz-landing-system : lando

testing/xpcshell/remotexpcshelltests.py

@@ -473,7 +473,7 @@ class XPCShellRemote(xpcshell.XPCShellTests, object):
         # The tests directory can be quite large: 5000 files and growing!
         # Sometimes - like on a low-end aws instance running an emulator - the push
         # may exceed the default 5 minute timeout, so we increase it here to 10 minutes.
-        self.initDir(self.remoteScriptsDir)
+        self.device.rm(self.remoteScriptsDir, recursive=True, force=True, timeout=None, root=True)
         self.device.push(self.xpcDir, self.remoteScriptsDir, timeout=600)
         self.device.chmod(self.remoteScriptsDir, recursive=True, root=True)