libtest: add assert_log_message_value_by_name() function

Signed-off-by: Balazs Scheidler <balazs.scheidler@balabit.com>
libtest: fix compilation warning in assert_msg_field_equals_non_fatal()

WIP: a very similar function is available in msg_parse_lib
db-parser: fixed compilation warning about a stray space in a string literal

Signed-off-by: Balazs Scheidler <balazs.scheidler@balabit.com>
db-parser: split inherit-properties testcase into 2 smaller functions

And simplify their fixture patterndb a lot.

Signed-off-by: Balazs Scheidler <balazs.scheidler@balabit.com>
db-parser: create new _construct_message_with_nvpair() function in test_patterndb
db-parser: add msg_matches to output msg assertions
nvtable: add nv_table_is_value_set() function

Signed-off-by: Balazs Scheidler <balazs.scheidler@balabit.com>
logmsg: implement log_msg_merge_context()
db-parser: implement inherit-properties='context' for patterndb actions

This patch implements a new choice for inherit-properties that will merge
all name-value pairs into the new synthetic message, with the most recent
being beferred over older values.

Tags are not being merged, right now the last message determines
the set of tags that are assigned to the new message.

Signed-off-by: Balazs Scheidler <balazs.scheidler@balabit.com>
Merge pull request #291 from balabit/f/inherit-property-context

F/inherit property context