Fix: missing variant choice name

Fix: missing variant choice name

While running ust clock override tests:

ok 19 - Start tracing for session clock_override
ok 20 - Application done
ok 21 - Stop lttng tracing for session clock_override
ok 22 - Destroy session clock_override
08-03 16:28:19.082 996505 996505 E PLUGIN/CTF/META/PARSER yyerror@parser.ypp:927 At line 52 in metadata stream: syntax error, unexpected CTF_RBRAC: token="}"
08-03 16:28:19.082 996505 996505 E PLUGIN/CTF/CTF-1-META-STREAM-PARSER [fs] Cannot create the metadata stream AST from TSDL text: ret=1
08-03 16:28:19.083 996505 996505 E PLUGIN/SRC.CTF.FS [fs] Failed to exectute query: object=babeltrace.support-info
08-03 16:28:19.083 996505 996505 W LIB/QUERY-EXECUTOR bt_query_executor_query@query-executor.c:231 Component class's "query" method failed: query-exec-addr=0x5614fe4204a0, cc-addr=0x5614fe41b690, cc-type=SOURCE, cc-name="fs", cc-partial-descr="Read CTF traces from the file sy", cc-is-frozen=0, cc-so-handle-addr=0x5614fe4188d0, cc-so-handle-path="/usr/local/lib/babeltrace2/plugins/babeltrace-plugin-ctf.la", object="babeltrace.support-info", params-addr=0x5614fe4218b0, params-type=MAP, params-element-count=2, log-level=WARNING
08-03 16:28:19.083 996505 996505 E CLI-CFG-SRC-AUTO-DISC support_info_query_all_sources@autodisc.c:493 babeltrace.support-info query failed.
08-03 16:28:19.083 996505 996505 E CLI main@babeltrace2.c:2653 Command-line error: retcode=1

ERROR:    [Babeltrace CLI] (babeltrace2.c:2653)
  Command-line error: retcode=1
CAUSED BY [Source auto-discovery] (autodisc.c:493)
  babeltrace.support-info query failed.
CAUSED BY [libbabeltrace2] (query-executor.c:231)
  Component class's "query" method failed: query-exec-addr=0x5614fe4204a0,
  cc-addr=0x5614fe41b690, cc-type=SOURCE, cc-name="fs", cc-partial-descr="Read
  CTF traces from the file sy", cc-is-frozen=0,
  cc-so-handle-addr=0x5614fe4188d0,
  cc-so-handle-path="/usr/local/lib/babeltrace2/plugins/babeltrace-plugin-ctf.la",
  object="babeltrace.support-info", params-addr=0x5614fe4218b0, params-type=MAP,
  params-element-count=2, log-level=WARNING
CAUSED BY ['source.ctf.fs'] (fs.cpp:1598)
  Failed to exectute query: object=babeltrace.support-info
CAUSED BY ['source.ctf.fs'] (ctf-1-metadata-stream-parser.cpp:462)
  Cannot create the metadata stream AST from TSDL text: ret=1
CAUSED BY [CTF metadata parser] (parser.ypp:927)
  At line 52 in metadata stream: syntax error, unexpected CTF_RBRAC: token="}"

Cause
=====

The name of the variant choice is missing.

Solution
========

Output the field name followed by ";" as defined by the spec.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Change-Id: I166c92d659b6c74dfaf5ee20ac5d74c9f1a808a8