Tests requiring ledger support should be skipped by default

[aaronc]

Tests requiring ledger support always run when using go test ./... or my IDE and always fail because ledger support isn't enabled by default.

We should either filter these out with the existing ledger build tag or use some flag to skip them.

Here's a list of such tests:

[julienrbrt]

It seems like it was done purposely (?):

cosmos-sdk/crypto/ledger/ledger_notavail.go

Line 17 in 417ce25

return nil, errors.New("support for ledger devices is not available in this executable")