test: create directory for certs before copying

[dotnwat]

Cover letter

If the directory in which certs are copied to does not exist then an
error will be thrown. This PR ensure the target directory exists before
copying the cert files.

Fixes: #4552

Testing. I suppose other issues could cause this, but I simulated this scenario by manually manipulating paths and it produced the same error. Further, bootstrap config writing also initializes the target directory suggesting this may have been encountered before.

Release notes

• none

[dotnwat]

/backport v22.1.x

[vbotbuildovich]

The pull request is not merged yet. Cancelling backport...

[abhijat]

Was about to ask if we should check if dir exists before creating to avoid an error but it looks like this function uses mkdir -p so should be fine

    def mkdirs(self, path, mode=_DEFAULT_PERMISSIONS):
        self.ssh("mkdir -p %s && chmod %o %s" % (path, mode, path))

[dotnwat]

Failures are existing:

• test: failure in rptest.tests.mirror_maker_test.TestMirrorMakerService.test_simple_end_to_end.source_type #4317
• Timeout in ManyPartitionsTest (ManyPartitionsTest.test_many_partitions) #4373

[dotnwat]

/backport v22.1.x