Exclude 'target' and '.DS_Store' from checkstyle coverage (typedb#390)

## What is the goal of this PR?

We now exclude `target` and `.DS_Store` from checkstyle coverage tests.

## What are the changes implemented in this PR?

`target` is typically a generated folder (e.g. by `cargo`). `.DS_Store`
is generated by Finder on a Mac. They should be excluded from checkstyle
coverage.

NB: Fixing typedb#253 would
remove the need for this PR, but it's harder to do.

tool/checkstyle/test-coverage.py

@@ -36,6 +36,7 @@ def try_decode(s):
     workspace_files, _ = tc.shell_execute([
         'find', '.',
             '(', '-name', '.git',
+            '-o', '-name', '.DS_Store',
             '-o', '-name', '.idea',
             '-o', '-name', '.ijwb',
             '-o', '-name', '.github',
@@ -44,6 +45,7 @@ def try_decode(s):
             '-o', '-name', 'VERSION',
             '-o', '-name', '*.md',
             '-o', '-name', 'node_modules',
+            '-o', '-name', 'target',
         ')', '-prune', '-o', '-type', 'f', '-print'
     ], cwd=os.getenv("BUILD_WORKSPACE_DIRECTORY"))
     workspace_files = workspace_files.split()