Make tests work with vault 0.7.x

[pschultz]

Starting with Vault 0.7 list operations always use paths with a trailing
slash, so the policy used in testing has to allow that path in addition
to the one without a trailing slash.

Link to changelog, see first item under DEPRECATIONS/CHANGES.

The github.com/hashicorp/vault/api package is outdated too. Let me know if you'd like me to update (although there is no particular reason to do so).

[pschultz]

I should mention that the tests still work with 0.6:

--- PASS: TestVaultSource (4.55s)
        source_test.go:304: Starting /home/pschultz/bin/vault-0.6.5: "Vault v0.6.5 ('5d8d702f33b5fd965cbe8d6d0728295de813a196')\n"
    --- PASS: TestVaultSource/renewable_token (0.76s)
    --- PASS: TestVaultSource/non-renewable_token (0.60s)
    --- PASS: TestVaultSource/renewable_orphan_token (0.74s)
    --- PASS: TestVaultSource/non-renewable_orphan_token (0.74s)
    --- PASS: TestVaultSource/renewable_wrapped_token (0.93s)
    --- PASS: TestVaultSource/non-renewable_wrapped_token (0.61s)
PASS
ok      github.com/fabiolb/fabio/cert   4.555s

[magiconair]

Thank you so much! :)