Introduce a metadata file listing all core plugins

With this commit we add a new metadata file called "core-plugins.txt"
which contains all Elasticsearch core plugins and not just the ones that
can be used with Rally out-of-the-box (i.e. without additional
configuration).

Relates elastic/rally#309

plugins/core-plugins.txt

@@ -0,0 +1,35 @@
+########################################################################
+#
+# This config file is used for Rally >= 0.7.3.
+#
+# It contains the names of all plugins that are part of Elasticsearch
+# core. Some of them require custom configuration and will not work
+# out of the box (see x_pack for an example on how to create a custom
+# plugin configuration).
+#
+########################################################################
+analysis-icu
+analysis-kuromoji
+analysis-phonetic
+analysis-smartcn
+analysis-stempel
+analysis-ukrainian
+# 'discovery-*' requires custom config
+discovery-azure-classic
+discovery-ec2
+discovery-file
+discovery-gce
+ingest-attachment
+ingest-geoip
+ingest-user-agent
+lang-javascript
+lang-python
+mapper-attachments
+mapper-murmur3
+mapper-size
+# 'repository-*' requires custom config
+repository-azure
+repository-gcs
+repository-hdfs
+repository-s3
+store-smb

plugins/official-plugins.txt

@@ -1,3 +1,13 @@
+########################################################################
+#
+# This config file is used for older versions of Rally (before 0.7.3)
+#
+# It contains all plugins that are part of Elasticsearch core. However,
+# we exclude plugins that require custom configuration here as they
+# could not be used out of the box.
+#
+#
+########################################################################
 analysis-icu
 analysis-kuromoji
 analysis-phonetic