upgrade: Restore leapp environment variables on --resume

[vinzenz]

This patch will restore leapp environment variables from the IPUConfig
message. This will allow to easier and more naturally access environment
from actors during the upgrade even after reboot etc.

Signed-off-by: Vinzenz Feenstra vfeenstr@redhat.com

[github-actions]

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[MichalHe]

I've tested this PR in the following manner:
An actor that runs in the FirstBoot phase and prints the environment was added to the code in the source branch of this PR. The actor code:

import os

from leapp.actors import Actor
from leapp.libraries.stdlib import api
from leapp.tags import FirstBootPhaseTag, IPUWorkflowTag


class PrintEnvinronment(Actor):
    """
    Docs
    """

    name = 'print_environment'
    consumes = ()
    produces = ()
    tags = (FirstBootPhaseTag, IPUWorkflowTag)

    def process(self):
        api.current_logger().debug('Environmental variables: {0}'.format(os.environ))

Then leapp was executed as follows using the internal RHEL7 vagrant box:

LEAPP_TEST_VARIABLE_RESTORE_WORKS=some_value leapp upgrade --debug --reboot

The produced (truncated) logs:

...
2021-09-24 15:04:03.410 DEBUG    PID: 5936 leapp.workflow.FirstBoot.print_environment: Environmental variables: environ({'LANG': 'en_US.UTF-8', 'PATH': '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/etc/leapp/repos.d/system_upgrade/el7toel8/tools', 'INVOCATION_ID': '<ID>', 'TERM': 'vt220', , 'LEAPP_HOSTNAME': '<HOSTNAME>', 'LEAPP_DEBUG': '1', 'LEAPP_VERBOSE': '1', 'LEAPP_EXPERIMENTAL': '0', 'LEAPP_UNSUPPORTED': '1', 'LEAPP_NO_RHSM': '1', 'LEAPP_COMMON_TOOLS': ':/etc/leapp/repos.d/system_upgrade/el7toel8/tools:/etc/leapp/repos.d/system_upgrade/el7toel8/tools', 'LEAPP_COMMON_FILES': ':/etc/leapp/repos.d/system_upgrade/common/files:/etc/leapp/repos.d/system_upgrade/el7toel8/files:/etc/leapp/repos.d/system_upgrade/common/files:/etc/leapp/repos.d/system_upgrade/el7toel8/files', 'LEAPP_EXECUTION_ID': '<EXECUTION_ID>', 'LEAPP_TEST_VARIABLE_RESTORE_WORKS': 'some_value', 'LEAPP_CURRENT_PHASE': 'FirstBoot', 'LEAPP_CURRENT_ACTOR': 'print_environment'})
...

[MichalHe]

lgtm.

[pirat89]

lgtm and otuput from @MichalHe looks good too