daemon: fix racy tests caused by copy-pasted variable

The test creates two symbolic links but reuses some information about them by
passing the same variable. Use the proper variable to avoid being sensitive to
symlink mtime differences on fast enough systems.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>

daemon/api_snaps_test.go

@@ -1800,7 +1800,7 @@ components:
 				InstallDate: snap.ComponentInstallDate(cpi, snap.R(7)), InstalledSize: 2},
 			{Name: "comp-2", Type: "test", Version: "1.0", Revision: snap.R(34),
 				Summary: "summary 2", Description: "description 2",
-				InstallDate: snap.ComponentInstallDate(cpi, snap.R(7)), InstalledSize: 3},
+				InstallDate: snap.ComponentInstallDate(cpi2, snap.R(7)), InstalledSize: 3},
 			{Name: "comp-3", Type: "test",
 				Summary: "summary 3", Description: "description 3"},
 			{Name: "comp-4", Type: "test"},