Update Mopidy installer for Mopidy 3/Python 3

Note: At time of publishing Iris 3.44.0 is not available on pip, so Iris (3.43.0) will fail to start with Mopidy 3.x

- Drop specific package versions, so we don't have to continually maintain this install script. Not much point holding versions, since pypi packages could be updated and end up incompatible with our older held ones.
- Install python3 versions of dependencies
- Make sure apt unholds mopidy and mopidy-spotify to correct previous installations
- Run an --upgrade install on mopidy-iris so this script can- sort of- be used as an upgrader
- Divine Iris's system.sh location using pkg_resources and *always* update the sudoers file

mopidy/install.sh

@@ -3,12 +3,9 @@
 DATESTAMP=`date "+%Y-%m-%d-%H-%M-%S"`
 MOPIDY_CONFIG="/etc/mopidy/mopidy.conf"
 MOPIDY_SUDOERS="/etc/sudoers.d/010_mopidy-nopasswd"
-MOPIDY_SYSTEM_SH="/usr/local/lib/python2.7/dist-packages/mopidy_iris/system.sh"
 EXISTING_CONFIG=false
-PYTHON_MAJOR_VERSION=2
-MOPIDY_VERSION=2.3.1-1
-MOPIDY_SPOTIFY_VERSION=3.1.0-0mopidy1
-PIP_BIN=pip
+PYTHON_MAJOR_VERSION=3
+PIP_BIN=pip3
 
 function add_to_config_text {
     CONFIG_LINE="$1"
@@ -35,7 +32,7 @@ warning() {
 # Update apt and install dependencies
 inform "Updating apt and installing dependencies"
 apt update
-apt install -y python-rpi.gpio python-spidev python-pip python-pil python-numpy
+apt install -y python3-rpi.gpio python3-spidev python3-pip python3-pil python3-numpy
 echo
 
 # Verify python version via pip
@@ -93,22 +90,29 @@ fi
 
 # Install Mopidy and core plugins for Spotify
 inform "Installing mopidy packages"
-apt install -y --allow-downgrades mopidy=$MOPIDY_VERSION mopidy-spotify=$MOPIDY_SPOTIFY_VERSION
-apt-mark hold mopidy mopidy-spotify
+apt-mark unhold mopidy mopidy-spotify
+apt install -y mopidy mopidy-spotify
 echo
 
 # Install Mopidy Iris web UI
 inform "Installing Iris web UI for Mopidy"
-$PIP_BIN install mopidy-iris
+$PIP_BIN install --upgrade mopidy-iris
 echo
 
 # Allow Iris to run its system.sh script for https://github.com/pimoroni/pirate-audio/issues/3
 # This script backs Iris UI buttons for local scan and server restart.
-if [ ! -f "$MOPIDY_SUDOERS" ]; then
-  inform "Adding $MOPIDY_SYSTEM_SH to $MOPIDY_SUDOERS"
-  echo "mopidy ALL=NOPASSWD: $MOPIDY_SYSTEM_SH" > $MOPIDY_SUDOERS
-  echo
-fi
+
+# Get location of Iris's system.sh
+MOPIDY_SYSTEM_SH=`python$PYTHON_MAJOR_VERSION - <<EOF
+import pkg_resources
+distribution = pkg_resources.get_distribution('mopidy_iris')
+print(f"{distribution.location}/mopidy_iris/system.sh")
+EOF`
+
+# Add it to sudoers
+inform "Adding $MOPIDY_SYSTEM_SH to $MOPIDY_SUDOERS"
+echo "mopidy ALL=NOPASSWD: $MOPIDY_SYSTEM_SH" > $MOPIDY_SUDOERS
+echo
 
 # Install support plugins for Pirate Audio
 inform "Installing Pirate Audio plugins..."