Testsuite: Replace --version=x.y.z with package@x.y.z

Testsuite: Fix calls to die to always include line numbers ...

'die' actually taking two parameters seems to be a little-known fact.

Make 'dub remove' remove all packages by default in non-interactive mode ...

Given how often it is used in the test-suite, it should be self-obvious
that it will be what most users want.

Use a value < ushort.max for tests using the test_registry ...

It is possible for the PID to be >= 65536, in which case the dub_registry
would fail to parse the argument and error out.
This can be frequently experienced on long running systems,
for example Mac OSX.

Fix local cache