Call bash rather than sh in hostboot.mk; fails on ubuntu 14.04
diff --git a/openpower/package/hostboot/hostboot.mk b/openpower/package/hostboot/hostboot.mk
index 0d09702..5331c68 100644
--- a/openpower/package/hostboot/hostboot.mk
+++ b/openpower/package/hostboot/hostboot.mk
@@ -17,7 +17,7 @@
     OPENPOWER_BUILD=1 CROSS_PREFIX=$(TARGET_CROSS) HOST_PREFIX="" HOST_BINUTILS_DIR=$(HOST_BINUTILS_DIR) 
 
 define HOSTBOOT_BUILD_CMDS
-        $(HOSTBOOT_ENV_VARS) sh -c 'cd $(@D) && source ./env.bash && $(MAKE)'
+        $(HOSTBOOT_ENV_VARS) bash -c 'cd $(@D) && source ./env.bash && $(MAKE)'
 endef
 
 define HOSTBOOT_INSTALL_IMAGES_CMDS