Disable SDK keyval support tests on nexus

These are flaky but failing more often than not.  Disabling to prevent
masking other failures

Change-Id: Icccfeadb00f45947cbe2ccc4c9cb2e79cedb7982

shodan_boot.robot

diff --git a/shodan_boot.robot b/shodan_boot.robot
index 1633b2a..40dbaaf 100644
--- a/shodan_boot.robot
+++ b/shodan_boot.robot
@@ -38,6 +38,7 @@
 
 # TODO(sleffler): This test failed with debug artifacts.
 Test SDK keyval support (+SecurityCoordinator)
+    Skip if                     "${PLATFORM}" == "nexus"
     Requires                    shodan-bootup
     Install App                 keyval
     Wait For Line On Uart       read(foo) failed as expected