test: Enable specifying flaky tests on fips

[komawar]

Adds a way to mark a specified test as 'flaky' on fips compliant
systems.

Earlier, the tools/test.py script supported only 'mode',
'system' and 'arch' for test environment specification. This limits the
ability to specify the behavior of tests and setting pre-determined
behavior of the same on other types of systems. As an example, the
feature request below indicates the need to specify certain tests as
'flaky' on fips compliant systems. It hints at future possibility of a
shared library, which in turn may need a specifier for running tests.

This commit introduces a new item in the env dict, called type
which defaults to simple type. It also adds an optional command
line argument --type, which inputs strings. Current functionality
extends to setting simple or fips for this type variable.
However, extending it to further uses is rather simple by adding "if"
conditions at appropriate places in the tools/test.py script.

Fixes: #14746

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

• build
• doc
• test