Prevent tmt scripts from running outside of test context (teemtee#3833)

Now when scripts are moved, they are not ready to be executed anywhere
but in `execute`. Adding a short check to prevent them being used in
`prepare` or `finish`. I expected that will change gradually, e.g. there
is no reason to not use `tmt-abort` in `prepare` scripts, for example,
except its connection to `execute.

Part of the effort to implement teemtee#902.

Author: happz

tmt/steps/scripts/tmt-abort

@@ -1,4 +1,10 @@
 #!/bin/bash
+
+if [ -z "$TMT_TEST_PIDFILE" ]; then
+    echo "tmt-abort can be used only in the context of a running test."
+    exit 1
+fi
+
 # Create the abort file.
 touch "$TMT_TEST_DATA/abort"
 # Kill PPID to exit test execution.

tmt/steps/scripts/tmt-file-submit

@@ -1,4 +1,10 @@
 #!/bin/bash
+
+if [ -z "$TMT_TEST_PIDFILE" ]; then
+    echo "tmt-file-submit can be used only in the context of a running test."
+    exit 1
+fi
+
 set -o errexit -o pipefail -o noclobber -o nounset
 
 die() { echo "$*" >&2; exit 2; }  # complain to STDERR and exit with error

tmt/steps/scripts/tmt-reboot

@@ -1,5 +1,10 @@
 #!/bin/bash
 
+if [ -z "$TMT_TEST_PIDFILE" ]; then
+    echo "tmt-reboot can be used only in the context of a running test."
+    exit 1
+fi
+
 # Two-level reboot: `tmt-reboot` extracts command line arguments, and
 # calls `tmt-reboot-core` *while holding the tmt test pidfile lock!*
 # That should assure the pidfile would exist and contain valid info.

tmt/steps/scripts/tmt-report-result

@@ -1,4 +1,10 @@
 #!/bin/bash
+
+if [ -z "$TMT_TEST_PIDFILE" ]; then
+    echo "tmt-report-result can be used only in the context of a running test."
+    exit 1
+fi
+
 set -o errexit -o pipefail -o noclobber -o nounset
 
 REPORT_RESULT_OUTPUTFILE="$TMT_TEST_DATA/tmt-report-results.yaml"