Elasticsearch 5 split string type in two: keyword (also known as exact
in gerrit index type system) and text (also known as full text in gerrit
index type system). During migration from Elasticsearch 2 to 5 exact
type was erroneously split in exact and keyword types, that are the same.
This reverts commit 506125e71a786f31573e6ba1b1983a4c48cc1dbc.
This reverts commit 09fdc3eaadd352b628acfc95c5b74df305b9dbf9.
Change-Id: I788e4d06d490687508c4bfd1703037a268fe31a5
0f6c9bd34c