gitignore: ignore directories made on running jepsen tests

On running Jepsen tests created directory with Terraform state and directory
with Jepsen tests source code in a build directory. Everything is ok on using
out of source build in a separate directory, but with building in a project
root directory these directories appears in `git status` output. This patch add
ignores for these directories.

.gitignore

@@ -144,6 +144,10 @@ sftpscript.txt
 *.md5sum
 extra/deploy_key
 compile_commands.json
+jepsen-tests-prefix
+.terraform
+terraform.tfstate
+terraform.tfstate.backup
 
 # autogenerated files
 src/box/sql/keywordhash.h