introduce OPENGROK_SRC_ROOT for overriding source root

fixes #1789

Author: vladak

OpenGrok

@@ -18,6 +18,7 @@
 # Supported Environment Variables for configuring the default setup:
 #   - OPENGROK_DISTRIBUTION_BASE  Base Directory of the OpenGrok Distribution
 #   - OPENGROK_INSTANCE_BASE      Base Directory of the OpenGrok User Data Area
+#   - OPENGROK_SRC_ROOT		  directory with files to be indexed
 #   - OPENGROK_CTAGS              Full path to Exuberant or Universal CTags binary
 #   - OPENGROK_CTAGS_OPTIONS_FILE Full path to file with extra command line
 #                                 options for CTags program (for its --options
@@ -186,7 +187,11 @@ DefaultInstanceConfiguration()
 
     # REQUIRED: Source Code/Repository Root
     #           (your source code or the root of all repositories)
-    SRC_ROOT="${OPENGROK_INSTANCE_BASE}/src"
+    if [ -n "${OPENGROK_SRC_ROOT}" ]; then
+        SRC_ROOT="${OPENGROK_SRC_ROOT}"
+    else
+        SRC_ROOT="${OPENGROK_INSTANCE_BASE}/src"
+    fi
 
     # REQUIRED: OpenGrok Generate Data Root
     #           (for Lucene index and hypertext cross-references)