Adopt debcargo auto-gen'd testing stuff

Another thing generated that I'm just trusting is accurate. Oops.

debian/rules

@@ -1,4 +1,7 @@
 #!/usr/bin/make -f
 
 %:
-	dh $@ --buildsystem=cargo
+	dh $@ --buildsystem cargo
+
+override_dh_auto_test:
+	dh_auto_test -- test --all

debian/tests/control

@@ -0,0 +1,14 @@
+Test-Command: /usr/share/cargo/bin/cargo-auto-test gt-tool 3.0.1 --all-targets --all-features
+Features: test-name=rust-gt-tool:@
+Depends: dh-cargo (>= 31), rustc, @
+Restrictions: allow-stderr, skip-not-installable
+
+Test-Command: /usr/share/cargo/bin/cargo-auto-test gt-tool 3.0.1 --all-targets
+Features: test-name=librust-gt-tool-dev:default
+Depends: dh-cargo (>= 31), rustc, @
+Restrictions: allow-stderr, skip-not-installable
+
+Test-Command: /usr/share/cargo/bin/cargo-auto-test gt-tool 3.0.1 --all-targets --no-default-features
+Features: test-name=librust-gt-tool-dev:
+Depends: dh-cargo (>= 31), rustc, @
+Restrictions: allow-stderr, skip-not-installable