mapr: fix the discovery of the version of Scala

The structure of the page changed slightly between July 8th
and now (thanks Internet Archive).
Adapt the extraction code. including a more robust regex.

Also update the download location (lightbend.com instead of
typesafe.com, even if the latter is still a redirect).

Finally, expose a new variable which allows users to
force a specific version of Scala, disabling the autodetection.
This is useful to workaround possible future similar breakages
without changing the code.

Closes-Bug: #1704337

Change-Id: Ib105d08816d6833f05301e59f64163de5f070109
(cherry picked from commit 83c3011f69)

elements/hadoop-mapr/README.rst

@@ -37,3 +37,8 @@ DIB_MAPR_VERSION
   :Required: Yes
   :Description: Version of MapR to install.
   :Example: ``DIB_MAPR_VERSION=5.2.0``
+
+SCALA_VERSION
+  :Required: No
+  :Description: Force a specific version of Scala (disable autodetection).
+  :Example: ``SCALA_VERSION=2.12.2``

elements/hadoop-mapr/install.d/41-scala

@@ -17,11 +17,13 @@ if [ "$RETURN_CODE" != "200" ]; then
     echo "http://www.scala-lang.org is unreachable" && exit 1
 fi
 
-if [ "trusty" == "${DIB_RELEASE:-}" ]; then
+if [ -n "${SCALA_VERSION:-}" ]; then
+    VERSION=${SCALA_VERSION}
+elif [ "trusty" == "${DIB_RELEASE:-}" ]; then
     # scala >= 2.12 for ubuntu depends on openjdk-8, not available on trusty
     VERSION=${DEF_VERSION}
 else
-    VERSION="$(curl -s --fail http://www.scala-lang.org|grep 'scala-version'|grep -Eo '([0-9]\.?)+')"
+    VERSION="$(curl -s --fail http://www.scala-lang.org| tr -d '\n' | sed 's/^.*<div[^<]\+scala-version">[^0-9]\+\([0-9\.\?]\+\)<.\+$/\1/')"
 
     if [ $? != 0 -o -z "${VERSION}" ]; then
         echo "Installing default version $DEF_VERSION"
@@ -31,7 +33,7 @@ fi
 
 PKG=scala-${VERSION}
 
-URL="http://downloads.typesafe.com/scala/${VERSION}"
+URL="http://downloads.lightbend.com/scala/${VERSION}"
 
 if [ "$DISTRO_NAME" = "ubuntu" ]; then
     wget -N ${URL}/${PKG}.deb