Unpin PasteDeploy dependency version

Fixes bug #1133262

There are no newer releases of PasteDeploy than 1.5.0 and we have no
reason to believe newer versions will break us. Indeed, if an
incompatible version is released, we will want to know about it quickly.

Change-Id: I331b33b16ea50202886b19bf5c4060d9fa46d5ec
Replace direct tempfile usage with a fixture.

tempfiles should always be created in fixtures to ensure that they actually
get cleaned up when we're done.

Change-Id: If4eee03b2e9ec6bd5333b8d5022ec9809343584e
Merge "Replace direct tempfile usage with a fixture."
Merge "Unpin PasteDeploy dependency version"