317 bigquery using dbi

[javier-gracia-tabuenca-tuni]

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[javier-gracia-tabuenca-tuni]

this PR is for #317

Changes:

• ListTables.R: if dbms is 'bigquery' uses bigrquery:: function to list tables
• InsertTable.R: if dbms is 'bigquery' and if dropTableIfExists deletes table before inserting, bigrquery:: is not doing that correctly
• DBI.R: for a DatabaseConnectorDbiConnection if dbms is 'bigquery' uses delayIfNecessaryForDdl and delayIfNecessaryForInsert, just like it does for JDBC
• Sql.R: On the above delay function I had to fix the regex so that It works also when using .
  If there is an error and dbms is 'bigquery' take the error message from err$body, that contains the real sql error

Minor Changes:

• I added some skip to some test files. Tests assume to have a Postgress always set up which I dont have/needed only to test BQ. Please remove if needed.
• in the test-InsertTable.R: removed the filter for Bigquery is slow (Without bulk upload), bcs now it is fast

Doubts I got when applying the tests. Not sure If changing the test is the correct path:

• bigrquery doent return the columns in the same order that they have been inserted. I force the column order in the sql fetching the data
• bigrquery doesn't insert time zones. I force the InserTable to remove that from the dataframe before insertion.
• bigrquery lost precision when inserting floats. I changed the test to make an exception. Is that ok ??
• dbplyrTestFunction failed at Test slicing. I changed the test to make an exception. Is that ok ??

Still TO DO
At the moment I haven't defaulted the DatabaseConnector to use DBI. I set that in the setup.R

Im not sure what would be the best way to modify the DatabaseConnector:::connectBigQuery function
Particularly how to pass the 'billing' parameter
And you prefer to have 'bigrquery::bq_auth' with in the DatabaseConnector:::connectBigQuery. bigrquery::bq_auth() use different parameters depending on the environment.

I can work on that if you believe this is going correctly