Fixed 2 bugs + Added possibility to use credentials object for auth

[quentin-sommer]

Hi,

I am using the credentials config object option to authenticate against google cloud, as specified here.

This pr just propagates options.credentials to the datastore constructor when it is truthy, allowing to use this way of authenticating.

[quentin-sommer]

Well, digging more into the code I found 2 bugs that I fixed in https://github.com/bedeoverend/feathers-datastore/pull/9/commits/bbd83c5b90ff54a4e7f0b11534bc7086cbc54665 and https://github.com/bedeoverend/feathers-datastore/pull/9/commits/b1c25b747e9c9c8d08d511073108ef6990d40ac1

• bug 1 the key were only properly created for a single entity, but the bug failed silently resulting in a partial key creation
• bug 2 when sending multiple entities to create() the nonIndex options was lost when doing the recursion call to makeExplicitEntity, resulting in properties not being marked as excludeFromIndexes.

This had the side effect of improving feathers's test success rate

• before 72 passing 2 pending 33 failing
• after 78 passing 2 pending 27 failing

Would you like me to put them in a separate PR? I rely on this changes for my application to work. @bedeoverend

[bedeoverend]

Great, thanks @quentin-sommer!

[bedeoverend]

This is included in v0.1.7

[quentin-sommer]

Thanks!