Add support for creating a new testing environment in functions.sh

Add the new functions _run_env(), _exit_env(), _init_env() and
_cleanup_env() to run the tests inside a new environment specified with the
TST_ENV environment variable.

A typical structure of a script with tests is:

trap '_report_exit_and_cleanup _cleanup_env cleanup' \
    SIGINT SIGTERM SIGSEGV EXIT

cleanup() {
	<test cleanup>
}

<tests implementations>

_run_env "$TST_KERNEL" "$PWD/$(basename "$0")" "env_var1=$env_var1 ..."

_exit_env "$TST_KERNEL"

_init_env

<tests init>

<tests call>

If TST_ENV is not set or empty, don't create a new testing environment and
perform the cleanup in the current environment. Don't create a new testing
environment also if the script is already executed in a new environment, to
avoid loops. Instead, for cleanup, do it in the new environment and skip it
in the host environment (if the cleanup function is passed to
_cleanup_env()).

Signal to the creator of the environment failures of tests or of the script
itself run in the new environment (if the exit code is 1 ($FAIL) or 99
($HARDFAIL)) with an unclean shutdown of the system.

Add haveged and systemd as dependencies for the tests in ci/fedora.sh,
respectively for initializing the random number generator and for shutting
down the system in the new environment.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

ci/fedora.sh

@@ -45,7 +45,9 @@ yum -y install \
 	vim-common \
 	wget \
 	which \
-	zstd
+	zstd \
+	haveged \
+	systemd
 
 yum -y install docbook5-style-xsl || true
 yum -y install swtpm || true