Enable manual tests in CI:

Fixes: RIPD-1575. Fix argument passing to runner. Allow multiple unit
test selectors to be passed via --unittest argument. Add optional
integer priority value to test suite list. Fix several failing manual
tests. Update CLI usage message to make it clearer.

src/test/README.md

@@ -0,0 +1,30 @@
+
+# Unit Tests
+
+## Running Tests
+
+Unit tests are bundled in the `rippled` executable and can be executed using the
+`--unittest` parameter. Without any arguments to this option, all non-manual
+unit tests will be executed. If you want to run one or more manual tests, you
+must specify it by suite or full-name (e.g. `ripple.app.NoRippleCheckLimits` or
+just `NoRippleCheckLimits`).
+
+More than one suite or group of suites can be specified as a comma separated
+list via the argument. For example, `--unittest=beast,OversizeMeta` will run
+all suites in the `beast` library (root identifier) as well as the test suite
+named `OversizeMeta`). All name matches are case sensitive. 
+
+Tests can be executed in parallel using several child processes by specifying
+the `--unittest-jobs=N` parameter. The default behavior is to execute serially
+using a single process.
+
+The order that suites are executed is determined by the suite priority that 
+is optionally specified when the suite is declared in the code with one of the
+`BEAST_DEFINE_TESTSUITE` macros. By default, suites have a priority of 0, and
+other suites can choose to declare an integer priority value to make themselves
+execute before or after other suites based on their specified priority value.
+
+By default, the framework will emit the name of each testcase/testsuite when it
+starts and any messages sent to the suite `log` stream. The `--quiet` option will
+suppress both types of messages, but combining `--unittest-log` with `--quiet`
+will cause `log` messages to be emitted while suite/case names are suppressed.