base: Add argument to Coroutine class to not run on creation

In some cases, the point where you create a Coroutine is not the same as
where you want to start running it (and want it to switch back to). This
leads to the unnecessary overhead of switching in and out of the
Coroutine. This change adds an optional boolean argument to the
constructor for the Coroutine class to allow for overriding the default
behavior of running the Coroutine upon creation, which in specific cases
can be used to avoid the unnecessary overhead and improve simulator
performance.

Change-Id: I044698f85e81ee4144208aee30d133bcb462d35d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18588
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>

base: Rename unit test cc files to be *.test.cc.

This makes the name easier to read, looks ok if the file is named with
underscores between words or not, is easy to grep for, and shouldn't
introduce any ambiguities in the file names.

Change-Id: I34b7bcccea2d87c10c0de417dd5e3ef27c4b5666
Reviewed-on: https://gem5-review.googlesource.com/c/14676
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>