More exhaustive assertions for native rule tag propagation tests

[Silic0nS0ldier]

In src/test/shell/bazel/tags_propagation_native_test.sh

• assert_contains_n "Command Line:" n output1
ExecutionInfo: { is inappropriate as TemplateExpand also have execution info.
• assert_contains_n "(local|no-cache|no-remote):" n output1
  Counting n increases confidence that all expected actions have the execution info they should have. e.g. tags propagated for tests, but not other actions when --incompatible_allow_tags_propagation=false
• --experimental_allow_tags_propagation -> --incompatible_allow_tags_propagation
  Addresses warnings in test logs.

Changes in src/test/shell/unittest.bash address a bug in assert_contains_n which on failure was using the wrong argument to refer to the input file. For consistency other places were also updated to use $file instead of the argument number.