x/ref: Restructure security packages

Here are the renamings:

security               -> lib/security
security/audit         -> lib/security/audit
security/flag          -> lib/security/securityflag
security/serialization -> lib/security/serialization

security/agent                -> services/agent
security/agent/agentd         -> services/agent/agentd
security/agent/keymgr         -> services/agent/keymgr
security/agent/server         -> services/agent/server
security/agent/cache          -> services/agent/internal/cache
security/agent/lru            -> services/agent/internal/lru
security/agent/pingpong       -> services/agent/internal/pingpong
security/agent/test_principal -> services/agent/internal/test_principal

Note that the restructuring is not done, even after this CL is
submitted.  In particular, services/agent is supposed to contain
the *.vdl files, and the client and server libraries are supposed
to live in services/agent/agentlib, per our conventions.  Also
lib/unixfd can also be moved under services/agent/internal.  That
will be fixed in a subsequent CL.

MultiPart: 1/3
Change-Id: Ie9b14083d133a661f0d3a6c33a3ae05e3bac3cd2
diff --git a/test/modules/modules_test.go b/test/modules/modules_test.go
index 82a13cc..79ca03c 100644
--- a/test/modules/modules_test.go
+++ b/test/modules/modules_test.go
@@ -22,14 +22,14 @@
 
 	"v.io/v23"
 	"v.io/v23/verror"
-
 	"v.io/x/ref/envvar"
 	"v.io/x/ref/lib/exec"
-	_ "v.io/x/ref/profiles"
-	vsecurity "v.io/x/ref/security"
+	vsecurity "v.io/x/ref/lib/security"
 	"v.io/x/ref/test"
 	"v.io/x/ref/test/modules"
 	"v.io/x/ref/test/testutil"
+
+	_ "v.io/x/ref/profiles"
 )
 
 func init() {
diff --git a/test/modules/shell.go b/test/modules/shell.go
index d72010e..729c360 100644
--- a/test/modules/shell.go
+++ b/test/modules/shell.go
@@ -158,8 +158,8 @@
 	"v.io/v23/security"
 	"v.io/x/ref/envvar"
 	"v.io/x/ref/lib/exec"
-	"v.io/x/ref/security/agent"
-	"v.io/x/ref/security/agent/keymgr"
+	"v.io/x/ref/services/agent"
+	"v.io/x/ref/services/agent/keymgr"
 	"v.io/x/ref/test/expect"
 )
 
diff --git a/test/modules/util.go b/test/modules/util.go
index ca6f5c3..a19e8b9 100644
--- a/test/modules/util.go
+++ b/test/modules/util.go
@@ -13,10 +13,9 @@
 	"os"
 	"strings"
 
-	vsecurity "v.io/x/ref/security"
-
 	"v.io/v23/security"
 	"v.io/x/lib/vlog"
+	vsecurity "v.io/x/ref/lib/security"
 )
 
 func newLogfile(prefix, name string) (*os.File, error) {