restore initial environment before processing each easystack item

[bedroge]

Closes #4194 by explicitly restoring the environment at the end of build_and_install_software. This should prevent that the dependencies of a previous (set of) installation(s) are still loaded for the next one, e.g. when using an easystack file. Also added a test that verifies this.

Test output before applying the patch to main.py:

$ python3 -O -m test.framework.easystack
.......F..
======================================================================
FAIL: test_easystack_restore_env_after_each_build (__main__.EasyStackTest)
Test that the build environment is reset for each easystack item
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/bob/ebdev/easybuild-framework/test/framework/easystack.py", line 148, in test_easystack_restore_env_after_each_build
    self.assertFalse(regex.search(stdout), "Pattern '%s' should not be found in: %s" % (regex.pattern, stdout))
AssertionError: <re.Match object; span=(166129, 166280), match="WARNING Loaded modules detected: ['EasyBuild-deve> is not false : Pattern 'WARNING Loaded modules detected: \[.*gompi/2018.*\]\n' should not be found in:
<LOTS OF OUTPUT>
== 2023-02-10 13:46:59,710 easyblock.py:2248 WARNING Loaded modules detected: ['EasyBuild-develop', 'GCC/6.4.0-2.28', 'hwloc/1.11.8-GCC-6.4.0-2.28', 'OpenMPI/2.1.2-GCC-6.4.0-2.28', 'gompi/2018a']
<LOTS OF OUTPUT>
----------------------------------------------------------------------
Ran 10 tests in 2.169s

FAILED (failures=1)

After applying the patch:

$ python3 -O -m test.framework.easystack
..........
----------------------------------------------------------------------
Ran 10 tests in 2.096s

OK

[bedroge]

Tests are failing because of:

ERROR: test_compiler_cache (test.framework.toolchain.ToolchainTest)
Test ccache
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/runner/736df0562413dad6f69227f3175ee31db19c4876/lib/python2.7/site-packages/test/framework/toolchain.py", line 2187, in test_compiler_cache
    self.assertTrue(os.path.samefile(os.environ['CCACHE_DIR'], ccache_dir))
  File "/opt/hostedtoolcache/Python/2.7.18/x64/lib/python2.7/UserDict.py", line 40, in __getitem__
    raise KeyError(key)
KeyError: 'CCACHE_DIR'

But I have no clue what's causing this, doesn't seem related to this PR?

[boegel]

@bedroge That test is failing because in it we assume that the build environment does not get reset after the installation of easyconfigs, which the change you propose (which does make sense) is breaking...

[boegel]

@bedroge The failing test is actually telling us that we're making a somewhat intrusive change.
It's not impossible that some people are actually relying on the build environment not being reset, for example when using EasyBuild as a library.

Here's a proposal for a different approach: bedroge#1

[bedroge]

@bedroge The failing test is actually telling us that we're making a somewhat intrusive change. It's not impossible that some people are actually relying on the build environment not being reset, for example when using EasyBuild as a library.

Here's a proposal for a different approach: bedroge#1

Looks good, merged!

[boegel]

lgtm