Reduce code duplication in multiple copies of test_env.py.

Reduce code duplication in multiple copies of test_env.py.

Do not eliminate all the copies (yet).

This changed the default version from 'default-version' to 'v1a' and app name
from whatever in app.yaml to 'sample-app'. Updated a few tests accordingly.

Rename replica_app to test_replica_app. It makes it clear it's a test_ and will
be caught by skip_files rule once it's moved out of tests/.

R=vadimsh@chromium.org
BUG=

[M-A, 2015-03-19 01:24:30]

Depends on https://codereview.appspot.com/215360043

[Omondo1, 2023-12-27 03:03:13]

Publish all my draft

[Omondo1, 2023-12-27 03:10:11]

On 2015/03/19 01:24:30, M-A wrote:
> Depends on https://codereview.appspot.com/215360043

[Omondo1, 2023-12-27 03:10:20]

On 2023/12/27 03:10:11, Omondo1 wrote:
> On 2015/03/19 01:24:30, M-A wrote:
> > Depends on https://codereview.appspot.com/215360043

[Omondo1, 2023-12-27 03:10:21]

On 2023/12/27 03:10:11, Omondo1 wrote:
> On 2015/03/19 01:24:30, M-A wrote:
> > Depends on https://codereview.appspot.com/215360043

[Omondo1, 2023-12-27 03:10:30]

On 2023/12/27 03:10:21, Omondo1 wrote:
> On 2023/12/27 03:10:11, Omondo1 wrote:
> > On 2015/03/19 01:24:30, M-A wrote:
> > > Depends on https://codereview.appspot.com/215360043

[Omondo1, 2023-12-27 07:59:09]

On 2023/12/27 03:10:30, Omondo1 wrote:
> On 2023/12/27 03:10:21, Omondo1 wrote:
> > On 2023/12/27 03:10:11, Omondo1 wrote:
> > > On 2015/03/19 01:24:30, M-A wrote:
> > > > Depends on https://codereview.appspot.com/215360043