[lldb] update TestEchoCommands

Followup to https://reviews.llvm.org/D112988

Sorry, I broke this test.   The test was verifying the bad behavior
of --source-quietly that the previous change fixed -- namely that
it still echos the initial list of startup commands while
sourcing them.

Updated the test to verify that --source-quietly is quiet, rather than
loud.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D113047