functional-tests: Fix installation errors in install.sh script

- On Debian 10, pin pytest-bdd version to 3.2.1, this is the latest
  version that supports pytest 3.10.1.
- Install wheel and pytest-xdist packages from the Debian repos.
- Add git as a dependency for functional tests.
- Fix regexp when getting Gecko version from the Github api, for some
  reason after colon, sometimes there is a space and sometimes not.

Tests performed on Debian stable, testing and unstable:
- Installing dependencies with the install.sh script succeeds.
- No regressions when running tests.

Signed-off-by: Veiko Aasa <veiko17@disroot.org>

plinth/tests/functional/install.sh

@@ -4,16 +4,23 @@ IFS=$'\n\t'
 
 echo "Installing requirements"
 sudo apt-get install -yq --no-install-recommends \
-    python3-pytest python3-pytest-django \
-    python3-pip firefox-esr smbclient\
+    python3-pytest python3-pytest-django python3-pytest-xdist \
+    python3-pip python3-wheel firefox-esr git smbclient\
     xvfb
-pip3 install wheel
-pip3 install splinter pytest-splinter pytest-bdd pytest-xvfb pytest-xdist
+
+if [ $(lsb_release --release --short) == '10' ]
+then
+    pip3 install pytest-bdd==3.2.1
+else
+    pip3 install pytest-bdd
+fi
+
+pip3 install splinter pytest-splinter pytest-xvfb
 
 echo "Installing geckodriver"
 (
     DL_DIR=/tmp/gecko
-    GECKO_VERSION=$(curl --silent "https://api.github.com/repos/mozilla/geckodriver/releases/latest" | grep -Po '"tag_name": "\K.*?(?=")')
+    GECKO_VERSION=$(curl --silent "https://api.github.com/repos/mozilla/geckodriver/releases/latest" | grep -Po '"tag_name":\s*"\K.*?(?=")')
     FILENAME="geckodriver-${GECKO_VERSION}-linux64.tar.gz"
     GECKO_URL="https://github.com/mozilla/geckodriver/releases/download/$GECKO_VERSION/$FILENAME"