Duplicate pin uses name of the old one

[lidel]

> ipfs pin remote add --service=mock --name=failed-test bafybeie7xsekwthhvpoybij6wlouifh2dpt2l6aouehj3tvnrejigpqgnq
Error: remote service failed to pin requestid="req-2"

> ipfs pin remote add --service=mock --name=pinned-test bafybeie7xsekwthhvpoybij6wlouifh2dpt2l6aouehj3tvnrejigpqgnq
CID:    bafybeie7xsekwthhvpoybij6wlouifh2dpt2l6aouehj3tvnrejigpqgnq
Name:   failed-test
Status: pinned

I believe mock should allow duplicate pins, as long they have a different name, or at least override the name of the existing one (this should be enough for use in tests)