Suggestion: Add a way to specify the test name to capsule test.

[jordanmack]

Describe the bug
There is no way to specify the test that should be run using capsule test. This would be helpful to filter the tests that are executed. This is supported in Cargo with cargo test <testname>.

Additional context
username@dev1:~$ capsule --version
Capsule 0.4.4

[TheWaWaR]

The suggestion way to run contract tests is:

# Test debug version of the contract
$ CAPSULE_TEST_ENV=debug cargo test -p tests
# Test release version of the contract
$ CAPSULE_TEST_ENV=release cargo test -p tests

Since capsule test is just a proxy of above command.