ewaol-tests: Add password reset to tests which access Guest VM user account

This patch resets the user account password on the Guest VM before and after the
relevant test suites execute. The password reset only occurs on virtualization
images which have been security hardened via the ewaol-security DISTRO_FEATURE.
The password reset is added by having security-specific code override the
extra_cleanup function which is called only by virtualization-specific code,
achieved via conditional appends to the test suites in the recipes.

With this mechanism for conditional inclusion of code to the BATS scripts
aligned across the test suites, the special substring-replace for
K3S_LOAD_VIRT_FUNCS has been dropped.

As the conditionally-appended code may not be just tests but also additional
function and variable definitions, the files are renamed from
"additional-*-tests.bats" to "append-*.bats.

This patch also adds a new runtime test internal variable 'TEST_GUEST_VM_NAME'
that takes the value assigned to test specific global variable:
'[CE|VIRT|K3S|UA]_TEST_GUEST_VM_NAME'.

Issue-Id: SCM-4421
Signed-off-by: Kamil Dziezyk <kamil.dziezyk@arm.com>
Signed-off-by: Richard Neill <richard.neill@arm.com>
Change-Id: Iaa7664e27812280238668fc0e7fea1c0fa018f34