Use luafilesystem to change directory

In some circumstances, if not every syscall was somehow redefined, the
directory was not changed correctly. With luafilesystem.chdir it is
assured that we are in the wanted directory afterwards.

spec/awful/completion_spec.lua

@@ -6,6 +6,7 @@ end
 local gfs = require("gears.filesystem")
 local Gio = require("lgi").Gio
 local GLib = require("lgi").GLib
+local lfs = require("lfs")
 
 local has_bash = GLib.find_program_in_path("bash")
 local has_zsh = GLib.find_program_in_path("zsh")
@@ -60,12 +61,14 @@ end
 
 describe("awful.completion.shell in empty directory", function()
     local orig_popen = io.popen
+    local orig_dir = lfs.currentdir()
 
     setup(function()
         test_dir = get_test_dir()
         io.popen = function(...)  --luacheck: ignore
             return orig_popen(string.format('cd %s && ', test_dir) .. ...)
         end
+        lfs.chdir(test_dir)
         test_path = get_test_path_dir()
     end)
 
@@ -73,6 +76,7 @@ describe("awful.completion.shell in empty directory", function()
         assert.True(os.remove(test_dir))
         io.popen = orig_popen  --luacheck: ignore
         remove_test_path_dir(test_path)
+        lfs.chdir(orig_dir)
     end)
 
     if has_bash then
@@ -92,6 +96,7 @@ end)
 
 describe("awful.completion.shell", function()
     local orig_popen = io.popen
+    local orig_dir = lfs.currentdir()
 
     setup(function()
         test_dir = get_test_dir()
@@ -102,6 +107,7 @@ describe("awful.completion.shell", function()
         io.popen = function(...)  --luacheck: ignore
             return orig_popen(string.format('cd %s && ', test_dir) .. ...)
         end
+        lfs.chdir(test_dir)
         test_path = get_test_path_dir()
     end)
 
@@ -112,6 +118,7 @@ describe("awful.completion.shell", function()
         assert.True(os.remove(test_dir))
         io.popen = orig_popen  --luacheck: ignore
         remove_test_path_dir(test_path)
+        lfs.chdir(orig_dir)
     end)
 
     if has_bash then