tests/unit/go: allow skipping of gofmt checks on 19.10

Ubuntu 19.10 comes with Go 1.11 where gofmt produces formatting that is
incompatible with earlier releases. However, we enforce go 1.10 formatting rules
on Travis. Allow gofmt checks to be skipped on these systems.

Signed-off-by: Maciej Borzecki <maciej.zenon.borzecki@canonical.com>

tests/unit/go/task.yaml

@@ -18,7 +18,18 @@ execute: |
     rm -r /tmp/static-unit-tests/src/github.com/snapcore/snapd/vendor/*/
     rm -rf /tmp/static-unit-tests/src/github.com/snapcore/snapd/cmd/{autom4te.cache,configure,test-driver,config.status,config.guess,config.sub,config.h.in,compile,install-sh,depcomp,build,missing,aclocal.m4,Makefile,Makefile.in}
 
-    su -l -c "cd /tmp/static-unit-tests/src/github.com/snapcore/snapd && PATH=$PATH GOPATH=/tmp/static-unit-tests ./run-checks --static" test
+    if [[ "$SPREAD_SYSTEM" == ubuntu-19.10-* ]]; then
+        # the code is formatted according to gofmt 1.10 rules, but those changed
+        # in later releases; skip gofmt checks on systems where go is known to
+        # be newer and produce incompatible formatting
+        skip='SKIP_GOFMT=1'
+    fi
+
+    su -l -c "cd /tmp/static-unit-tests/src/github.com/snapcore/snapd && \
+        PATH=$PATH GOPATH=/tmp/static-unit-tests \
+        ${skip:-} \
+        ./run-checks --static" test
+
     su -l -c "cd /tmp/static-unit-tests/src/github.com/snapcore/snapd && \
         TRAVIS_BUILD_NUMBER=$TRAVIS_BUILD_NUMBER \
         TRAVIS_BRANCH=$TRAVIS_BRANCH \