Differentiate usages of word "include" in cc_sdk_test.go

A number of tests in cc_sdk_test.go use "include" for the input include
directory which results in the output containing "include/include"
(because the snapshot code uses "include" as the directory into which
native headers will be output). This change switches the inputs from
"include.." to "myinclude.." to differentiate between the two sources.

Bug: 180427921
Test: m nothing

Change-Id: Iba1e6d94647c74b31307b18254c03580e64c91cf