Reading the credentials from a config file doesn't work if SAFE_AUTH_* env vars are unset

[bochaco]

The following works with no issues:

$ export SAFE_AUTH_PASSWORD="aaaaaa"
$ export SAFE_AUTH_SECRET="bbbbb"
$ echo "{ \"secret\":\"$SAFE_AUTH_SECRET\", \"password\":\"$SAFE_AUTH_PASSWORD\" }" > myconfig.json
$ cat myconfig.json 
{ "secret":"bbbbb", "password":"aaaaaa" }
$ cargo run --features mock-network -- -c myconfig.json -i nnnnnnn -y
    Finished dev [unoptimized + debuginfo] target(s) in 0.45s
     Running `target/debug/safe_auth -c myconfig.json -i nnnnnnn -y`
Account was created successfully!
$ cargo run --features mock-network -- -c myconfig.json -y
    Finished dev [unoptimized + debuginfo] target(s) in 0.42s
     Running `target/debug/safe_auth -c myconfig.json -y`
Logged in the SAFE Network successfully!

But if the secret and password env vars are unset then the safe_auth throws an error stating that the account couldn't be found:

Warning! Storing your secret/password in plaintext in a config file is not secure.
[2019-04-29T22:41:54Z DEBUG safe_auth] Attempting to log in...
[2019-04-29T22:41:54Z WARN  safe_authenticator::client] Could not fetch account from the Network: CoreError(No such account - CoreError::RoutingClientError -> NoSuchAccount)
[2019-04-29T22:41:54Z ERROR safe_auth] safe_auth error: Failed to log in: CoreError(No such account - CoreError::RoutingClientError -> NoSuchAccount)

[bochaco]

The root cause is that we are not removing the enclosing " from the values read from the json file