fmf: Dependency installation robustification

Sync some improvements from cockpit-machines:

 * Unbreak running `tmt` in local trees with an already existing ./bots
   symlink.
 * Don't install all NPM packages, only chrome-remote-interface and sizzle.
 * Disable detection of affected tests, taking too long for real
   projects.

test/browser/run-test.sh

@@ -4,11 +4,21 @@ set -eux
 # tests need cockpit's bots/ libraries and test infrastructure
 cd $SOURCE
 git init
+rm -f bots  # common local case: existing bots symlink
 make bots test/common
 
-# only install a subset to save time/space
+# support running from clean git tree
+if [ ! -d node_modules/chrome-remote-interface ]; then
+    # copy package.json temporarily otherwise npm might try to install the dependencies from it
     rm -f package-lock.json  # otherwise the command below installs *everything*, argh
+    mv package.json .package.json
+    # only install a subset to save time/space
     npm install chrome-remote-interface sizzle
+    mv .package.json package.json
+fi
+
+# disable detection of affected tests; testing takes too long as there is no parallelization
+mv .git dot-git
 
 . /etc/os-release
 export TEST_OS="${ID}-${VERSION_ID/./-}"