Build: fix travis error from timeout. Refs monero-project#249.

* Add FORCE_CLEAN env variable

.travis.yml

@@ -1,6 +1,7 @@
 env:
   global:
   - GCC_VERSION=5
+  - FORCE_CLEAN=yes
   - secure: 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
 sudo: required
 dist: trusty
@@ -28,10 +29,10 @@ addons:
       name: monero-project/kovri
       description: The Kovri I2P Router Project
     notification_email: anonimal@i2pmail.org
-    build_command_prepend: export CC=gcc-${GCC_VERSION} CXX=g++-${GCC_VERSION} && make clean
+    build_command_prepend: export CC=gcc-${GCC_VERSION} CXX=g++-${GCC_VERSION} ${FORCE_CLEAN} && make clean
     build_command: make -j2 everything
     branch_pattern: coverity_scan
-before_script: export CC=gcc-${GCC_VERSION} CXX=g++-${GCC_VERSION}
+before_script: export CC=gcc-${GCC_VERSION} CXX=g++-${GCC_VERSION} ${FORCE_CLEAN}
 script: if [ "${COVERITY_SCAN_BRANCH}" != 1 ]; then make clean && make -j2 everything; fi
 notifications:
   email: false

Makefile

@@ -29,6 +29,7 @@
 #TODO(unassigned): improve this Makefile
 
 build = build/ # TODO(unassigned): make this more useful
+remove-build = rm -fr $(build)
 
 cmake = cmake -D CMAKE_C_COMPILER=$(CC) -D CMAKE_CXX_COMPILER=$(CXX)
 
@@ -77,9 +78,12 @@ help:
 	cd $(build) && $(cmake) -LH ../
 
 clean:
-	@echo "CAUTION: This will remove the build directory" ; \
-	read -r -p "Is this what you wish to do? (y/N)?: " CONTINUE; \
-	[ $$CONTINUE = "y" ] || [ $$CONTINUE = "Y" ] || (echo "Exiting."; exit 1;)
-	rm -fr $(build)
+	@echo "CAUTION: This will remove the build directory"
+	@if [[ $$FORCE_CLEAN = "yes" ]]; then $(remove-build); \
+	else read -r -p "Is this what you wish to do? (y/N)?: " CONTINUE; \
+	  if [ $$CONTINUE = "y" ] || [ $$CONTINUE = "Y" ]; then $(remove-build); \
+	  else echo "Exiting."; exit 1; \
+	  fi; \
+	fi
 
 .PHONY: all shared static upnp tests doxygen everything help clean