Update git submodules

* Update docs/submodules/yardstick from branch 'stable/fraser'
  - Merge "Convert SLA asserts to raises" into stable/fraser
  - Convert SLA asserts to raises

    This commit converts Python assertions to a custom exception in all
    places where SLA validation is checked with an assertion.

    This commit also fixes all emerged pylint errors.

    JIRA: YARDSTICK-966

    Change-Id: If771ed03b2cbc0a43a57fcfb9293f18740b3ff80
    Signed-off-by: Miikka Koistinen <miikka.koistinen@nokia.com>
    (cherry picked from 39f80e9b06395ae1515cfcf08508504ad4dd978a)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index eb54a9e..1e515b6 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit eb54a9e65e838e092e5acb5a8bd4119dd2e9f556
+Subproject commit 1e515b6cc3dd15c399f2663999c9734610494e5c